I tried NextSTEP, which needs the patches marked + above. Alas, this is not enough to make it run. Maybe it is because QEMU SCSI disk and ESP emulation are too fast.
I played with NextSTEP/sparc a few years ago and got the same impression. I've managed to get it boot into a single user mode, but it was unstable on disk operations. Just a simple dd if=/dev/sd0a of=/dev/null was able to get it hanging. And I think it was hanging in the kernel idle loop doing nothing.
If there were a Darwin/sparc ditribution, we could take a look, if it's really a bug in NextSTEP or in qemu-system-sparc. But I couldn't find such a distribution.